Short definition

To thaw a frozen pipe safely: open the faucet first, then apply gentle heat (hair dryer, heat tape, or hot wet towels) starting at the faucet and working back toward the frozen section. Never use an open flame — propane torches start house fires and crack pipes. Watch for splits as the ice melts; burst-on-thaw is common.

What it is

When water in a pipe freezes, it expands about 9% by volume. That expansion can push pipe walls past their stress limit and split them — but the split often doesn’t leak until the ice melts and pressure returns. Thawing is a careful process because the same pipe that’s frozen may already be cracked.

The procedure:

  1. Find the frozen section. Usually somewhere unconditioned — a vented crawl space, garage wall, exterior-wall stud bay, or attic vent stack. Visible frost on copper is a giveaway.
  2. Open the affected faucet. This is the most important step. An open faucet gives water and steam an exit and prevents pressure from building behind the ice as it melts.
  3. Apply heat starting at the faucet, working back toward the frozen section. Always thaw in this direction — if you thaw from the middle, melted water can’t escape and pressure rises against the still-frozen plug.
  4. Use safe heat sources, in this order:
    • Hair dryer on medium heat, kept moving.
    • Electric heat tape or a heat blanket wrapped around the pipe.
    • Hot wet towels reapplied as they cool.
    • A space heater pointed at the exposed area (close cabinet doors first).
  5. Never use an open flame. Propane torches and blowtorches cause house fires, crack soldered joints, and produce scalding water at the faucet. The trade learned this the hard way.
  6. Watch for splits. As the thaw reaches the cracked section, water sprays. Be ready to shut the main off at the meter or whole-house valve.

If the pipe is buried in a wall and you can’t get to it, call a plumber. They have infrared cameras and pipe-thawing transformers (machines that pass low-voltage current through the pipe to warm it from inside).

Why it matters to a homeowner

The Pacific Northwest gets one or two hard freeze events per winter. The January 2024 Arctic blast caused a wave of burst pipes across Western Washington — most happened on thaw, not during the freeze itself. Knowing the safe thaw procedure means the difference between catching a split before it floods the kitchen and discovering it via a soaked ceiling.

The single most common WA freeze-damage pattern is a hose left attached to a freeze-proof outdoor sillcock. The hose holds water in the bibb past the shutoff point, ice forms inside the wall, and the pipe splits behind the siding where you can’t see it. The damage shows up the first time the hose bibb is used in spring.

Common failure modes (post-thaw)

  • Burst on thaw. Pipe split during freeze, leaks once pressure returns. Most common WA pattern.
  • Hairline crack in CPVC. May leak 1–2 inches past the visible split — replace generously.
  • Hose-bib stem crack hidden in wall. Discovered only when the bibb is reopened in spring.
  • Frost-proof sillcock damaged because hose was left attached. Disconnect garden hoses before the first freeze.
  • Frozen vent stack (rare in Seattle, more common in Spokane). Less urgent — sewer gas may briefly enter house, but the stack thaws naturally.

Common variants

  • Active thaw vs. winterization. Thawing is reactive; winterization (insulating pipes, dripping faucets, disconnecting hoses) is the prevention.
  • Hair dryer (safe) vs. propane torch (dangerous). This is not a debate. Open flame is never the right tool.
  • Surface thaw vs. in-wall thaw. Visible frozen pipe — DIY. Hidden frozen pipe — call a pro with infrared and a pipe-thawing transformer.

Washington note

Western Washington’s typical freeze events are short (1–4 days) but severe — temperatures drop into the teens and stay there. The Cascadia housing stock includes a lot of homes built before exterior-wall plumbing was a code concern, so kitchen sinks on north-facing walls and bathrooms over uninsulated crawl spaces are the usual freeze points. Eastern WA freezes are colder, longer, and better-anticipated — Spokane homes are typically built with deeper-insulated supply runs and more interior plumbing.

The single highest-yield WA-specific freeze precaution: disconnect every garden hose by November 1. Frost-proof sillcocks rely on the shutoff being inside the warm wall, but a connected hose holds water on the cold side of the valve and freezes back into the bibb. This causes more WA freeze damage than any other single mistake.

If you arrive at a vacation cabin and find no water, run the safe thaw procedure on every exposed pipe — and watch the meter when you turn the main back on. Spinning means a burst somewhere; shut off and inspect before flooding starts.